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Experimental investigation of gradually-varied unsteady flow passed a circular pile
Abstract The flow field around a vertically mounted circular pile exposed to gradually-varied unsteady flow is experimentally investigated. Experiments were conducted in a 30 m-long and 1 m-wide recirculating flume equipped with a variable discharge pump. A circular cylinder with 9 cm diameter was used as the model pile. To understand the influence of accelerating and decelerating flow conditions, three unsteady cases with different unsteadiness degrees were tested as well as a reference steady flow case. The spatial and temporal variations of Reynolds-averaged velocity and turbulence characteristics around the pile, as well as undisturbed flow, were analyzed. Findings show that there are distinct differences between the tested gradually-varied unsteady flow cases and the reference steady flow case. The Reynolds-averaged velocity vs. TKE plots of undisturbed flow indicated a hysteresis effect, such that larger turbulence is generated during the falling stage of the flow compared to the rising stage. This hysteresis was considerably reduced in the pile wake, and even reversed hysteresis was seen at certain cases. The spatial variation of Reynolds-averaged velocity and turbulence in the peak instant of unsteady flow was qualitatively similar to that of steady flow, but quantitatively, turbulence, flow contraction, and velocity deficit in the near-wake region were smaller in the case of unsteady flow. Contrarily, the unsteady flow generated remarkably higher turbulence levels at further downstream in the pile wake. It is concluded that in the case of unsteady flow the pile behaves as if it has a more streamlined shape. The results were also interpreted from structure-bed interactions perspective, explaining the differences between the pile scour induced by steady and unsteady flow conditions.
Highlights The flow structures around a pile under gradually-varied unsteady flow were investigated experimentally. Three unsteady flow cases and a reference steady flow case were used. Turbulence in the pile wake is smaller in unsteady flow, but sustains farther downstream. Contraction at the sides and velocity deficit downstream of the pile is weaker in unsteady flow. Hysteresis between velocity and turbulence inherent in unsteady flow decreases in the wake of the pile.
Experimental investigation of gradually-varied unsteady flow passed a circular pile
Abstract The flow field around a vertically mounted circular pile exposed to gradually-varied unsteady flow is experimentally investigated. Experiments were conducted in a 30 m-long and 1 m-wide recirculating flume equipped with a variable discharge pump. A circular cylinder with 9 cm diameter was used as the model pile. To understand the influence of accelerating and decelerating flow conditions, three unsteady cases with different unsteadiness degrees were tested as well as a reference steady flow case. The spatial and temporal variations of Reynolds-averaged velocity and turbulence characteristics around the pile, as well as undisturbed flow, were analyzed. Findings show that there are distinct differences between the tested gradually-varied unsteady flow cases and the reference steady flow case. The Reynolds-averaged velocity vs. TKE plots of undisturbed flow indicated a hysteresis effect, such that larger turbulence is generated during the falling stage of the flow compared to the rising stage. This hysteresis was considerably reduced in the pile wake, and even reversed hysteresis was seen at certain cases. The spatial variation of Reynolds-averaged velocity and turbulence in the peak instant of unsteady flow was qualitatively similar to that of steady flow, but quantitatively, turbulence, flow contraction, and velocity deficit in the near-wake region were smaller in the case of unsteady flow. Contrarily, the unsteady flow generated remarkably higher turbulence levels at further downstream in the pile wake. It is concluded that in the case of unsteady flow the pile behaves as if it has a more streamlined shape. The results were also interpreted from structure-bed interactions perspective, explaining the differences between the pile scour induced by steady and unsteady flow conditions.
Highlights The flow structures around a pile under gradually-varied unsteady flow were investigated experimentally. Three unsteady flow cases and a reference steady flow case were used. Turbulence in the pile wake is smaller in unsteady flow, but sustains farther downstream. Contraction at the sides and velocity deficit downstream of the pile is weaker in unsteady flow. Hysteresis between velocity and turbulence inherent in unsteady flow decreases in the wake of the pile.
Experimental investigation of gradually-varied unsteady flow passed a circular pile
Kohandel Gargari, Mehrnoush (author) / Kirca, V.S. Ozgur (author) / Yagci, Oral (author)
Coastal Engineering ; 168
2021-05-22
Article (Journal)
Electronic Resource
English
Gradually Varied Unsteady Flow
Wiley | 2021
|Springer Verlag | 2022
|Springer Verlag | 2008
|COMPUTATION OF GRADUALLY VARIED FLOW
Springer Verlag | 2022
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